The invention relates to controlling roaming in a mobile system.
A general packet radio service GPRS is a new service in the GSM (Global System for Mobile Communication) and it is one of the items being standardized at the ETSI (European Telecommunication Standard Institute). The GPRS operational environment consists of one or more sub-network service areas that are interconnected by a GPRS backbone network. A sub-network comprises a number of packet data service nodes, which are herein called GPRS support nodes and each one of which is connected to the GSM mobile network, for example to a mobile switching centre MSC, allowing them to provide mobile data terminals with packet data service via several base stations, i.e. cells. An intermediate mobile network provides circuit-switched or packet-switched data transmission between a support node and mobile stations. Different sub-networks, in turn, are connected to an external data network, for example to a packet switched public data network PSPDN. The GPRS service can thus be used for achieving packet data transmission between mobile stations and external data networks, with the GSM network acting as an access network. One of the features of the GPRS service network is that it operates almost independently of the GSM network.
The GSM/GPRS mobile system usually comprises two databases including data on mobile subscribers: a home location register HLR, which comprises data on all subscribers of the mobile system and the services subscribed by them, and a visitor location register VLR, which comprises data on mobile stations roaming the area of a given mobile switching centre MSC. Within this application, the concept “roaming” should be understood to mean the attachment of a mobile subscriber to an alien mobile system (or a network of an alien mobile system), i.e. other than the subscriber's home mobile system, thus allowing the subscriber to use at least some of the services provided by said alien mobile system. When a mobile subscriber moves to the area of an alien mobile system and tries to attach thereto, the alien mobile system checks from the home location register of the subscriber's home system if the subscriber is entitled to roam said system. If the mobile station supports both circuit-switched (e.g. GSM) and packet-switched GPRS functions, it will try to attach to both the GSM network and the GPRS network. As regards the GSM network, the access request is relayed to the mobile switching centre MSC, which checks from the home location register of the subscriber's home system if the subscriber's roaming is allowed. Similarly, as regards the GPRS network, the access request is relayed to the serving GPRS support node SGSN, which also checks from the home location register of the subscriber's home system if the subscriber's roaming is allowed. In accordance with prior art, the home location register gives the same reply to the inquiries made by both network elements (MSC and SGSN).
The problem in the above arrangement is that there may be for instance an agreement between the operator maintaining the subscriber's home system and the operator maintaining the alien system that entitles the subscriber to the use of only one network (or some networks), e.g. a GSM network or a GPRS network, of the alien system, but not all networks. In this case it should be possible to allow the subscriber to attach to the network(s) of the alien system allowed to the subscriber, and, on the other hand, to prevent the subscriber from attaching to the network(s) of the alien system not allowed to the subscriber. However, this is impossible in the prior art arrangement, which does not distinguish between the different networks comprised by a mobile system.